To provide a working method capable of giving a fine hole to a thin sheet or a thin tubular material without generating defects, such as burr and breakage, which are generated in pressing and shearing.

In the method, an impression is formed on the surface of a workpiece, and a fine hole having the same shape as the cross section of the bottom of the impression is given to the workpiece without generating burr, breakage, and the like by dissolving and removing the backside of the impression so that the impression penetrates through the workpiece. In a second step, the surface in the side where the impression is formed is preferably covered with a coating material that is insoluble in an etching solution. A slit hole or a comb-like shape is also formed by making the shape of the impression a line. Further, an error in a hole diameter caused by an error in the amount of dissolution is reduced by giving the tip end of a projection tool a parallel part that has the same cross section as the shape of the hole.